The Seismogenic Structure Of Ms 5.9 Balinzuoqi Earthquake And The Preliminary Study On The Delineation Of Potential Seismic Sources In The Daxing'anling Uplift

Less attention has been paid to the study of seismic tectonics of the Daxing'anling Uplift because of the location in the area of low seismicity in the past. However, the distribution as belts or clusters for moderate and small earthquakes clearly indicates modern crustal movement. There is a high frequency of moderate earthquake in this area, especially, two 5.9 earthquake took place in 2003 and 2004 respectively, which is beyond our understanding.According to analysis of the characteristic of tectonic deformation in late Cenozoic in the target area, we infer that the tectonic movement is represented by gradually uplifting. The main geotectonic curve is characterized by NE trend. The causative tectonics is controlled by the interaction of NE trend and NW trend.The determination of seismogenic structure is of importance in seismic hazard analysis (SHA). It is challenging as to the identification of seimogenic structure of moderate earthquake. It's absolutely well-marked that the 2003 Balinzuoqi MS5.9 earthquake occurred because of the low seismicity of the whole Daxing'anling Uplift. The penetrating research of conditions that"2003 event"took place, which can make sense to the understanding of seimogenic structure of Daxing'anling Uplift. According to the evidences derived geologically in the target area, we find the distribution of fault caused the 2003 earthquake, that is, the Shuiquanzigou-Xishanwan-Tianshankou fault cut the stratum of 498±49Ka which dated by ESR, showing property of left-lateral normal. meanwhile, we acquire the latest active information of the seismogenic fault based on the materials collection of geophysics and seismology related to this event and the interpretation of remote sensing images.Seismicity and geotectonic movement are characterized by intergrowth. Earthquakes often occurred along active tectonic zones, such as boundaries between different geotectonic units, including the margins of great depressions with development of secondary depressions. Along the boundaries of great uplifts with exposures of Quaternary volcanic rocks, moderate strong earthquake also easily occurred. Moderate strong earthquake often occurred along the regional Quaternary active fault zones. The regional faults on the margin of great uplifts (such as the Daxing'anling Uplift) with the development of secondary basins, even though they did not show clear activity in the Quaternary, may be the occurrence sites for earthquake with M = 5-5~1/2. For example, in the Wulagai Basin, Hulunhu faulted Basin, some earthquakes with M=5.0 or so have occurred. Moderate strong earthquakes are related to the clustered zones of recent small earthqukes. For recent moderate strong earthquakes, the clustered zones can show the scale of seismic focus. Historical moderate strong earthquake were generally related to the intersection between seismic zones of small earthquakes though sometimes the cluster of small earthquake was not clear. In the Quaternary buried regions, the secondary Cenozoic faulted depressions where recent small earthquakes occurred frequently are also the seismogenetic sites for moderate strong earthquakes. The Quaternary fault zones with the exposures of Cenozoic basaltic rocks, and the clustered belts of modern small earthquakes are all the occurrence sites of moderate strong earthquakes.